Φ(01) =  1
Φ(02) =  1, prime
Φ(03) =  2, prime
Φ(04) =  2
Φ(05) =  4, prime
Φ(06) =  2
Φ(07) =  6, prime
Φ(08) =  4
Φ(09) =  6
Φ(10) =  4
Φ(11) = 10, prime
Φ(12) =  4
Φ(13) = 12, prime
Φ(14) =  6
Φ(15) =  8
Φ(16) =  8
Φ(17) = 16, prime
Φ(18) =  6
Φ(19) = 18, prime
Φ(20) =  8
Φ(21) = 12
Φ(22) = 10
Φ(23) = 22, prime
Φ(24) =  8
Φ(25) = 20

25 primes =< 100
168 primes =< 1000
1229 primes =< 10000
9592 primes =< 100000